Behaviour of Small Fatigue Cracks in CU-5.5NI-1.28SI Alloy Round-Bar Specimens

Abstract

Cu-5.5Ni-1.28Si alloy processed by air-cooling after solution heat treatment was conducted to prevent the generation of discontinuous precipitates which bring a detrimental effect on mechanical properties, and stress-controlled fatigue tests were carried out at room temperature. The change in the surface damage during stressing was monitored by means of both direct observation and plastic replication technique, showing the crack initiation at grain boundaries, crystallographic slip planes and twin boundaries. The growth rate of a small crack can be determined by a term σa n l when n = 5.4, not by the stress intensity factor range.

MICROSTRUCTURE AND FATIGUE PROPERTIES OF CU–NI–SI ALLOY STRENGTHENED BY NI2SI INTERMETALLIC COMPOUNDS

“…where C 1 and n are material constants. The studies on small crack growth behaviour in various metals and alloys, such as carbon steels [21], low alloy steels [22], aluminium alloys [23], Ni-based superalloys [24], copper [25] and copper alloys [26], indicated that dl/dN of a small surface-crack in smooth specimens is determined by the term σ a n l. shows the growth data of a small surface-crack with the dl/dN vs. σ a n l correlation. The value of n in eqn (1) was 5.3 in all specimens.…”